This relates generally to circuits used in logic chains or systems and more particularly to a method of testing indeterminate outputs of cascode circuits with a DC test.
Certain implementations of logic circuits exhibit defect characteristics which significantly complicate the level of testing required of such circuits. Any defect which causes the product level to become indeterminate, i.e., of the same voltage level, is particularly impossible to detect with a DC test. When one circuit in a logic chain has an indeterminate output the operation of the next circuit in the logic chain is unpredictable. Hithertofore, any such indeterminate output was untestable by standard DC testing techniques since the response for such defective circuits was unpredictable.
The present invention is therefore directed toward a logic circuit that can be tested for defects within the circuit which would normally create indeterminate outputs. Moreover by modification of the circuit in accordance with the present invention such testing can be done with a simple DC stuck fault test.
In particular the invention describes a cascode circuit that can be tested for defects that normally create indeterminate outputs with a simple DC stuck fault test.